This invention relates to a broad class of high temperature composite materials that consist, essentially, of two distinct phases--a ceramic-like matrix which can be one of many different silicate-based geopolymers and a homogeneous dispersion of organic/inorganic additives of various shapes and dimensions. Individually, these two phases are generally unsuitable for high temperature applications, however, they combine in the composite form to produce a wide spectrum of refractory materials. More particularly, this invention relates to ambient cured, controlled density, advanced geopolymer composites whose macroscopic physical properties can be tailored for specific applications, over significant temperature ranges, by judicious specifications of dispersed phase components and selective chemical modifications to pre-gelled geopolymer resins. The invention also relates to process-dependent methods for fabricating such advanced geopolymer composites.
Particulate additives or "fillers" are sometimes added to high temperature materials to impart certain characteristics such as strength, flexibility or insulation. These fillers often include mineral glasses or fibrous reinforcers. Many naturally occurring mineral glasses, i.e., amorphous silica, contain sufficient chemically bound water to facilitate steam production upon melting. This causes the glass to expand into a very low density cellular aggregate, in a sense, an inorganic foamed material. Perlite is a popular volcanic glass which expands to very low density particles and is often used in the expanded form as a composite additive/filler in conjunction with sodium silicate binders, gypsum plasters, and Portland cements. These inorganic composites form low density, low thermal conductivity, insulating materials.
Fiber reinforcement of Portland cements, gypsum plasters, and sodium silicate binders is one method of enhancing the strength of inorganic materials. Fiberglass, mineral wool, and certain new ceramic refractory fibers have also been employed; however, the strong alkaline nature of these cements often produces considerable damage to the fibers. Alkaline resistant fiberglass has been developed and marked; however, many of these fibers are not easily bonded with inorganic cements. Water soluble foaming agents have also been added to various inorganic materials to enhance air entrainment and further reduce density.
Over the past several decades, industry has shown a preference for low cost petrochemical and thermoplastic hydrocarbon substitutes over inorganic materials. Typical examples include: foam plastic insulation substitutes for fiberglass and mineral wool; latex/acrylic modified cements and stuccoes; and synthetic substitutes for gypsum products. Some of these substitutions produce very desirable properties and advantages, however, in most cases, the substituted products increase fire and smoke hazards due to the combustibility of substituted ingredients.
In general, although organic materials have certain advantageous features which commend themselves to specific applications, these uses are usually attended by increased fire risk and smoke production when compared to their traditional inorganic counterparts. Therefore, it would be desirable to provide a class of material composites which incorporates significant proportions of both organics and inorganics. It would further be desirable to limit the combustibility of these composites to a level generally associated with inorganics while taking advantage of the desired physical properties of the organic constituents. In this manner, product designers can benefit from the advantages of organic fibers, foam fillers, etc., while enjoying the assurance of limited combustibility, non-toxicity, and energy conservation.